The present invention relates to a circuit for providing saw-tooth current in a coil, in particular the horizontal deflection coil of a cathode ray tube, and for storing part of the energy taken from a supply source, in particular for supplying at least one relatively-low-voltage auxiliary circuit, particularly in a television receiver. The circuit is designed for direct supply from a relatively-high-voltage source, obtained, in particular, by rectifying the alternating mains voltage, and comprises a parallel resonant circuit consisting of said deflection coil and which acts during the retrace interval of the saw-tooth, a first capacity and a second capacity which condition the trace interval and the retrace interval of the saw-tooth respectively, and in which, during the first part of the trace interval, current flows in a first diode connected parallel to the said retrace interval capacitance and, during the second part, in a second diode connected to the first and in a controllable electronic switch connected in series to the second diode, and to whose control electrode pulses are sent periodically to make it conductive for part of the trace interval and in which energy taken from a relatively-high-voltage source is stored in a first inductor, connected to said switch, when the latter is conductive, and transferred, at least partly, to the said resonant circuit, through a third capacitance, during the interval in which the said circuit is not conductive.
Circuits of this type are not unknown (see German Pat. No. 2,130,902, for example) and are very interesting, particularly for makers of television receivers, in that they provide a simple means, using a single switching device which is usually a transistor, of horizontal deflection and supply of low-voltage auxiliary circuits (12 or 25 Volt for example) starting directly with the d.c. voltage obtained by rectifying the 220 V (rms) a.c. domestic mains voltage. The known circuits, such as the one described in the aforementioned German patent or those described in French Pat. No. 2,208,259, use a secondary winding to transfer the energy from the said first inductor to the deflection circuit during the retrace interval; the power for supplying auxiliary circuits can be obtained by introducing further secondary windings and diodes rectifying the pulses produced therein.
As yet, these known circuits have not found any application in practice owing to practical difficulties such as the necessity for two transformers (one for supplying energy to the deflection circuit and to any other auxiliary circuits and one for generating high voltage for the kinescope) and the presence of a sharp initial variation in voltage at the terminals of the switch, when it ceases to be conductive, equal to the supply voltage, or of a high, and therefore undesirable, instantaneous current peak in the switch when it is closed.